CN115390185A - Valley edge state waveguide adopting armchair boundary and application thereof - Google Patents
Valley edge state waveguide adopting armchair boundary and application thereof Download PDFInfo
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Abstract
The invention discloses a valley edge waveguide adopting an armchair boundary and application thereof, and two boundaries with opposite structures are designed. Gu Bianyuan mode waveguide comprises an armchair boundary consisting of an SSBB form boundary and a BBSS form boundary; along the preset direction, the SSBB form boundary is sequentially formed by the boundary between two adjacent small regular triangle holes and the boundary between two adjacent large regular triangle holes, and the BBSS form boundary is sequentially formed by the boundary between two adjacent large regular triangle holes and the boundary between two adjacent small regular triangle holes. The valley edge state waveguide in the scheme can realize the directional selective transmission of the chiral optical field signal, and the chiral conservation is always kept in the transmission process. The combination of the zigzag boundaries allows for 90 ° and 180 ° signal turns. Meanwhile, by constructing a vertical crossing structure of the armchair boundary and the zigzag boundary, the beam splitting function of uniform intensity distribution of chiral light field signals at the vertical crossing point can be realized.
Description
Technical Field
The invention relates to the field of optical waveguide transmission, in particular to a valley edge waveguide adopting an armchair boundary and application thereof.
Background
An optical waveguide (optical waveguide) is a dielectric device that guides light waves to propagate therein, and is also called a dielectric optical waveguide. The loss of optical signals in optical waveguides during transmission is a significant problem in current optical communication and photonic integrated chips. Such losses can be caused by a number of factors: such as defects introduced in the preparation process of the optical waveguide, loss caused when the optical signal in the optical waveguide is transmitted at a large-angle rotation angle, loss introduced by the related beam splitting device for splitting the optical signal in the optical waveguide, and the like. These losses can cause the intensity of the transmitted optical signal to be attenuated and the optical signal to be diffused, which can easily cause the content of the transmitted optical signal to be distorted and captured and monitored.
The technical principle of topologically protecting the two-dimensional photonic crystal valley edge state waveguide is derived from quantum valley Hall effect of electrons in condensed state physics. The single-layer graphene can exist stably and has high electron mobility and the linear dispersion characteristic of a Dirac cone. In the research of two-dimensional materials, people adopt various methods to open a dirac cone of graphene so as to form an energy band gap, which is more beneficial to the application of the graphene materials in semiconductor devices.
In analogy to electronic systems, one can also construct such valley topology protected edge states in photonic systems to form optical waveguides to achieve back-scattering free and loss free transmission of photons. Starting from a photonic crystal structure of photonic graphene, constructing a required Dirac cone, and breaking the symmetry of spatial inversion, so that an energy band at the Dirac cone is opened to form an energy valley of the required photonic crystal. Based on the flexibility of the preparation process, the photonic graphene structure is most easily realized by a method for punching on the surface of the silicon material.
In the prior art, a two-dimensional circular hole is used for realizing optical signal transmission of a valley edge waveguide. However, the circular hole scheme has a problem that its energy band gap is an indirect band gap. The indirect band gap causes the energy valley extreme values not to be at the same inverted lattice position, and noise at the edges of the transmission spectrum passband of the photonic crystal appears.
In the prior art, the transmission of low-loss straight lines and 120-degree and 60-degree rotation angles of optical signals near 1560nm is realized by utilizing a valley edge state protected by a zigzag topology. Meanwhile, a circular optical microcavity is constructed by utilizing a valley edge waveguide formed by a two-dimensional graphene-like photonic crystal with a regular triangular hole, so that the screening and extraction of 1569.5nm optical signal high-quality factor signals are realized. However, based on the intersection of the two zigzag boundaries, researchers have discovered a phenomenon of beam splitting in which the intensities of the chiral optical signals are unequal, and a phenomenon of optical signal transmission path selection that can conserve valley chirality.
In summary, the zigzag boundary is used to realize the transmission of the chiral optical signal corner of 0 °, 60 ° and 120 °. Corner transmission valley edge mode waveguides at other angles cannot be realized. In addition, in a valley edge waveguide beam splitter formed by crossing two zigzag boundaries, the intensities of two separated optical signals are not equal, and the splitting function of equally splitting the chiral optical signal intensity cannot be realized.
Disclosure of Invention
In view of this, the present invention provides a valley edge state waveguide using armchair boundary and its application, the specific scheme is as follows:
the first part is that the invention provides a valley edge state waveguide adopting an armchair boundary, which is constructed in a graphene-like two-dimensional photonic crystal based on valley spin; the graphene-like two-dimensional photonic crystal comprises two hexagonal lattice primitive cells with opposite structures, namely a first hexagonal lattice primitive cell and a second hexagonal lattice primitive cell;
each hexagonal lattice primitive cell is composed of six sub-lattices in total, wherein one sub-lattice is composed of large regular triangle holes, and the other sub-lattice is composed of small regular triangle holes;
the Gu Bianyuan state waveguide comprises an armchair boundary, which can be divided into an SSBB form boundary and a BBSS form boundary;
defining a preset direction, a first direction and a second direction in the same plane, wherein the first direction and the second direction are respectively vertical to the preset direction and opposite to each other;
along the preset direction, the SSBB form boundary is sequentially formed by a boundary between two adjacent small regular triangle holes and a boundary between two adjacent large regular triangle holes, the first hexagonal lattice primitive cell is positioned in the first direction of the SSBB form boundary, and the second hexagonal lattice primitive cell is positioned in the second direction of the SSBB form boundary;
along predetermineeing the direction, BBSS form boundary comprises the boundary between two adjacent big regular triangle holes and the boundary between two adjacent little regular triangle holes in proper order, and the second hexagonal lattice primitive cell is located the first direction on BBSS form boundary, first hexagonal lattice primitive cell is located the second direction on BBSS form boundary.
In one embodiment, the hexagonal lattice primitive cell is a regular hexagon, and the side length of the hexagonal lattice primitive cell is a:
the range of the side length of the small regular triangle hole is 0.3a-0.45a, and the range of the side length of the large regular triangle hole is 0.5a-0.7a.
In one particular embodiment, the Gu Bianyuan state waveguide can transmit chiral optical signals;
the excitation source of the chiral light signal can be located at the center of any regular triangle hole in the armchair boundary.
In one embodiment, the excitation source can excite a chiral optical signal with a circularly polarized characteristic in the direction of the electric field, and the excitation source is divided into a left-handed chiral excitation source and a right-handed chiral excitation source according to the rotation direction of the circularly polarized electric field;
a left-handed chiral excitation source is arranged at the central position of a first small regular triangle hole on the boundary of the SSBB form, so that a chiral optical signal propagating leftwards can be excited;
a right-handed chiral excitation source is arranged at the central position of a first small regular triangle hole on the boundary of the SSBB form, so that a chiral optical signal propagating rightwards can be excited;
a left-handed chiral excitation source is arranged at the central position of the first large regular triangle hole on the BBSS form boundary, so that a chiral optical signal propagating leftwards can be excited;
a right-handed chiral excitation source is arranged at the center of the first large regular triangle hole on the boundary of the BBSS form, so that a chiral optical signal propagating rightwards can be excited.
In a specific embodiment, the Gu Bianyuan state waveguide further comprises a zigzag boundary;
the linking of the armchair borders with the zigzag borders allows to realize 90 ° corners and 180 ° corners of the signal.
In one embodiment, the zigzag border may be divided into a BB form border and an SS form border;
in a valley edge mode waveguide at a 90 ° corner:
if the armchair boundary in the horizontal direction is the SSBB type boundary:
the SS form boundary is jointed at the 90-degree corner of the SSBB form boundary, so that the right optical rotation signal can be upwards propagated along the SSBB form boundary;
by joining the boundaries of the SSBB forms at 90 ° corners of the boundaries of the SSBB forms, it is possible to realize that the right optical rotation signal propagates down the boundaries of the SSBB forms.
In one embodiment, a 180 ° turn of the dextrorotation signal is achieved by joining the zig-zag border at a 90 ° turn of the SSBB version border and joining the BBSS version border at a 90 ° turn of the zig-zag border.
The second part, the invention has proposed the transmission method of a chiral optical signal, adopt the stated trough edge state waveguide of the first part; the transmission method comprises the following steps:
an excitation source is arranged at the center of any regular triangle hole on the boundary of the armchair;
when the excitation source is a left-handed chiral optical signal, the optical signal is transmitted leftwards along the valley edge state waveguide; when the excitation source is a right-handed chiral optical signal, the optical signal is transmitted along the valley edge waveguide in the right direction; no back scattering signal returns in the transmission process and at the waveguide end face output;
the chiral optical signal enters the zigzag boundary at the 90-degree corner of the armchair boundary for transmission, so that the 90-degree corner of the chiral optical signal is realized; then enters the armchair boundary at a 90-degree corner of the zigzag boundary for transmission, and can realize a 180-degree corner of the chiral optical signal.
The invention provides a chiral optical signal equal splitting device based on a valley edge state waveguide, which comprises the valley edge state waveguide in the first part;
the beam splitting device comprises an SSBB form boundary, a BBSS form boundary, an SS form boundary and a BB form boundary, and an excitation source of a chiral optical signal is positioned at the SSBB form boundary or the BBSS form boundary;
in a preset first direction, the SSBB form boundary and the BBSS form boundary are connected at a preset beam splitting point;
in a preset second direction, the SS form boundary and the BB form boundary are connected at the beam splitting point;
the first direction is perpendicular to the second direction.
In one embodiment, after a chiral optical signal enters a beam splitting point from one type of armchair boundary, the chiral optical signal does not enter another type of armchair boundary based on the principle of chiral conservation;
and two forms of zigzag boundaries exist at the beam splitting point, and the transmission directions of the chiral optical signals in the two forms of zigzag boundaries after beam splitting are opposite, so that equal beam splitting is realized.
Has the advantages that: the invention discloses a valley edge state waveguide adopting an armchair boundary and application thereof, and a boundary formed by two-dimensional photonic crystals with opposite structures is designed to realize chiral optical signal transmission of the valley edge state waveguide under topological protection. The valley edge state waveguide constructed by the armchair boundary can realize the directional selective transmission of the chiral optical field signal, and the chiral conservation is always kept in the transmission process of the chiral optical signal. And the valley edge state waveguide constructed by combining the armchair boundary and the zigzag boundary can realize the transmission of a chiral optical field at a corner of 90 degrees and the transmission of a 180-degree corner formed by two continuous corners of 90 degrees, and no back scattering signal is lost in the transmission process. By constructing a vertical crossing structure of the armchair boundary and the zigzag boundary, a valley edge state waveguide beam splitting device protected by a two-dimensional photonic crystal topology is formed, and the beam splitting function of equally dividing the intensity of the transmitted chiral optical field signal at the vertical crossing point is realized.
Drawings
FIG. 1 is a schematic structural diagram of a valley edge waveguide in an embodiment of the present invention;
FIG. 2 is a diagram illustrating the transmission effect of a chiral optical signal in one direction according to an embodiment of the present invention;
FIG. 3 is a diagram illustrating the transmission effect of a chiral optical signal in another direction according to an embodiment of the present invention;
FIG. 4 is a diagram illustrating the transmission effect of a 90 ° rotation angle of a chiral optical signal according to an embodiment of the present invention;
FIG. 5 is a schematic structural diagram of a 90 ° rotation angle of a chiral optical signal according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of a 180 ° rotation angle of a chiral optical signal according to an embodiment of the present invention;
FIG. 7 is a schematic diagram illustrating an intensity-averaging beam splitting function of a chiral optical field formed by vertical crossing according to an embodiment of the present invention;
FIG. 8 is a schematic diagram illustrating an intensity-averaging beam splitting effect of a chiral optical field in an embodiment of the present invention.
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
Detailed Description
Hereinafter, various embodiments of the present disclosure will be described more fully. The present disclosure is capable of various embodiments and of being practiced with modification and alteration. However, it should be understood that: there is no intention to limit the various embodiments of the present disclosure to the specific embodiments disclosed herein, but rather, the disclosure is to cover all modifications, equivalents, and/or alternatives falling within the spirit and scope of the various embodiments of the present disclosure.
It should be noted that the scheme of the present invention is an edge state waveguide transmission scheme based on valley spin, and is different from the existing waveguide transmission scheme based on pseudo spin. The valley spin is that in the graphene crystal lattice, the C6 symmetry is broken, so that the band gap is opened at the high symmetry point K point of the inverted space. And two states of the band gap upper and lower correspond to two pseudo spins with opposite rotation properties.
In the present invention, a certain boundary may be represented in some form of a certain boundary. For example, the BBSS boundary may be represented as a BBSS form of an armchair boundary.
Because the edge state waveguide transmits light signals and needs to be captured in a dark environment, the experimental result graphs of the invention all use black as a background.
The terminology used in the various embodiments of the disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the various embodiments of the disclosure. As used herein, singular references are intended to include plural references unless the context clearly dictates otherwise. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the various embodiments of the disclosure belong. The terms (such as terms defined in commonly used dictionaries) should be interpreted as having a meaning that is the same as the context in the related art and will not be interpreted as having an idealized or overly formal meaning unless expressly so defined herein.
Example 1
The embodiment 1 of the invention discloses a valley edge state waveguide adopting an armchair boundary, which is designed with a boundary formed by two-dimensional photonic crystals with opposite structures by using the topological protection property of the valley edge state from the quantum valley Hall effect of photons so as to realize the chiral optical signal transmission of the valley edge state waveguide with topological protection. The Gu Bianyuan state waveguide has the structure shown in the attached figure 1 of the specification, and the specific scheme is as follows:
a valley edge state waveguide adopting armchair boundaries is constructed from a specific graphene-like two-dimensional photonic crystal based on the Gu Zixuan principle. The graphene-like two-dimensional photonic crystal can be obtained by a method of punching holes on the surface of a silicon material. The valley edge waveguide of the present embodiment is obtained based on a two-dimensional photonic crystal structure of a specific structure.
The graphene-like two-dimensional photonic crystal is formed by taking hexagonal lattice primitive cells as units. Each hexagonal lattice primitive cell is provided with six regular triangle holes which are distributed in the hexagonal lattice primitive cell in a graphene-like honeycomb form. There are two kinds of hexagonal lattice cells, which are the first hexagonal lattice cell and the second hexagonal lattice cell. The two hexagonal lattice primitive cells present opposite spatial structural characteristics, as shown in A1 and A2 in the attached figure 1 of the specification.
Each hexagonal lattice primitive cell is composed of six sub-lattices, wherein one sub-lattice is composed of large regular triangle holes, and the other sub-lattice is composed of small regular triangle holes. The space inversion symmetry of the honeycomb hexagonal lattice primitive cells is broken through by the two regular triangular holes with different sizes. In fig. 1, the hexagonal lattice primitive cell A1 and the hexagonal lattice primitive cell A2 exhibit opposite spatial structural characteristics, that is, the hexagonal lattice primitive cell A1 needs to perform spatial inversion around the center point of the primitive cell, or perform mirror image operation along the y-axis, so as to obtain the form of the hexagonal lattice primitive cell A2.
By linking the hexagonal lattice primitive cells A1 and a hexagonal lattice primitive cells A2 as shown in fig. 1, two forms of armchair boundaries, SSBB and BBSS, can be constructed. Gu Bianyuan mode waveguide is made up of a series of boundaries, the primary of which is the armchair boundary. According to morphology, the armchair boundary can be divided into an SSBB form boundary and a BBSS form boundary.
A preset direction, a first direction and a second direction are defined in the same plane, and the first direction and the second direction are respectively perpendicular to the preset direction and opposite in direction. The preset direction, the first direction and the second direction may be understood as a positive x-axis direction, a positive y-axis direction and a negative y-axis direction.
Along a preset direction (namely, a positive direction of an x axis), the SSBB form boundary is sequentially formed by a boundary between two adjacent small regular triangular holes and a boundary between two adjacent large regular triangular holes, and the first hexagonal lattice primitive cell is located in a first direction (namely, a positive direction of a y axis) of the SSBB form boundary, and the second hexagonal lattice primitive cell is located in a second direction (namely, a negative direction of the y axis) of the SSBB form boundary.
Along the preset direction (namely the positive direction of the x axis), the BBSS form boundary is sequentially formed by the boundary between two adjacent large regular triangle holes and the boundary between two adjacent small regular triangle holes, the second hexagonal lattice primitive cell is positioned in the first direction (namely the positive direction of the y axis) of the BBSS form boundary, and the first hexagonal lattice primitive cell is positioned in the second direction (namely the negative direction of the y axis) of the BBSS form boundary.
The armchair boundary is formed by the boundary between two adjacent congruent triangular holes, and the boundary types of SSBB (small size and big size) and BBSS (big and small size) are named according to the sequence from left to right. The optical signal is not completely limited on the boundary, a part of the signal is diffused to two sides, but the part of the signal is attenuated quickly, and the rest of the optical signal can only be transmitted along the boundary of the armchair. In fig. 1, the line of the B1 region is the SSBB boundary, and the line of the B2 region is the BBSS boundary. In the positive direction of the x-axis, the SSBB form refers to a small triangle, a large triangle, and a boundary between two small triangles and a boundary between two large triangles together constitute one SSBB boundary. The BBSS form is a large triangle, a small triangle and a small triangle, and the boundary between the two large triangles and the boundary between the two small triangles jointly form a BBSS boundary which is in an inverted structural form with the SSBB form. The upper part of the SSBB form is composed of hexagonal lattice primitive cells A1, and the lower part is composed of hexagonal lattice primitive cells A2; in contrast, above the BBSS form is a hexagonal cell A2, below which is a hexagonal cell A1.
The whole photonic crystal plate is made of silicon material, and holes are punched on the photonic crystal plate, so that the required photonic crystal structure and armchair boundary can be formed. The hexagonal lattice primitive cell is a regular hexagon, and the side length of the hexagonal lattice primitive cell is a, the side length range of the small regular triangle hole comprises 0.3a-0.45a, and the side length range of the large regular triangle hole comprises 0.5a-0.7a. Preferably, the side length of the small regular triangle shaped holes is 0.4a, and the side length of the large regular triangle shaped holes is 0.6a, as shown in fig. 1. Further preferably, a =423nm.
The valley edge state waveguide protected by the two-dimensional photonic crystal topology constructed on the boundary of the armchair can realize the directional selective transmission of chiral optical field signals, and the chiral conservation is always kept in the transmission process of the chiral optical signals. The excitation source of the chiral optical signal is located at the center of a regular triangle hole at the boundary of the armchair, and the regular triangle hole can be the center of any one of four regular triangle holes in the SSBB or BBSS format. The chiral optical signal of the excitation source is a chiral optical signal with a circularly polarized characteristic in the electric field direction, and the excitation source of the chiral optical signal can be classified into a left-handed chiral excitation source (counterclockwise rotation) and a right-handed chiral excitation source (clockwise rotation) according to the rotation direction of the circularly polarized electric field. The transmission process of the chiral optical signal in the valley edge state waveguide is shown in the specifications of figure 2 and figure 3.
A left-handed chiral excitation source is arranged at the central position of a first small regular triangle hole on the boundary of the SSBB form, so that a chiral optical signal propagating leftwards can be excited;
a right-handed chiral excitation source is arranged at the central position of a first small regular triangle hole on the boundary of the SSBB form, so that a chiral optical signal propagating rightwards can be excited;
a left-handed chiral excitation source is arranged at the central position of a first large regular triangle hole on the BBSS type boundary, so that a chiral optical signal propagating leftwards can be excited;
a right-handed chiral excitation source is arranged at the center of the first large regular triangle hole on the boundary of the BBSS form, so that a chiral optical signal propagating rightwards can be excited.
Experiments prove that the valley edge state waveguide of the embodiment is adopted to transmit the chiral optical signal, no back scattering signal returns in the transmission process and at the output of the end face of the waveguide, the characteristic that the Sarmchire armchair boundary valley edge state waveguide has the selective transmission of the chiral optical signal direction is verified, and the effect of inhibiting back scattering loss can be achieved.
In addition, the valley edge waveguide of the embodiment also comprises a zigzag boundary, and the zigzag boundary and the armchair boundary are combined to realize the turning of 90 degrees and 180 degrees of transmission signals. Specifically, combining the armchair border with a zigzag border link at a corner, a valley edge waveguide can be constructed that results in a 90 ° corner as well as a 180 ° corner. An excitation source can also be arranged in the zigzag boundary, so that the chiral optical signal starts from the zigzag boundary and enters the armchair boundary through the corner.
The zigzag boundary may be divided into a BB form boundary and an SS form boundary. The SS-shaped boundary is a zigzag boundary of zigzag-shaped two small regular triangular holes which are adjacent to each other. The BB form boundary is a zigzag boundary constructed of two adjacent opposing large regular triangular holes.
In a valley edge mode waveguide at a 90 ° corner: if the armchair boundary in the horizontal direction is the SSBB type boundary: the SS form boundary is jointed at the 90-degree corner of the SSBB form boundary, so that the right optical rotation signal can be upwards propagated along the SSBB form boundary; by joining the boundaries of the SSBB forms at 90 ° corners of the boundaries of the SSBB forms, it is possible to realize that the right optical rotation signal propagates down the boundaries of the SSBB forms. As shown in particular in fig. 4 and 5.
A 180 deg. turn can be achieved through two 90 deg. turns. The right turn signal 180 DEG turn can be realized by connecting the zigzag boundary at 90 DEG turn of SSBB form boundary and the BBSS form boundary at 90 DEG turn of zigzag boundary. The 180 ° angle is schematically shown in fig. 6.
Description figure 4 shows the experimental results of 90 ° rotation angle, and figure 5 is a schematic diagram of the transmission of optical signals in a valley edge state waveguide. The horizontal waveguides are SSBB form boundaries and then meet the SS form boundaries at a 90 ° corner. The right-handed chiral optical signal source is located at the center of a first small regular triangular hole on an SSBB form boundary, the frequency of the right-handed optical signal is 157.79THz, the right-handed optical field generated by excitation can only be transmitted rightwards along a valley edge waveguide, and is continuously transmitted upwards along an SS form boundary after undergoing a 90-degree corner, but no back scattering signal is generated although undergoing a 90-degree corner. Even if a 90 ° rotation angle is experienced once or twice in the chiral optical signal transmission path, no significant back-scattered signal is present in the valley edge state waveguide, demonstrating that the valley edge state waveguide of the present embodiment can transmit a chiral optical signal.
The embodiment discloses a valley edge waveguide adopting an armchair boundary, and a boundary formed by two-dimensional photonic crystals with opposite structures is designed to realize chiral optical signal transmission of the valley edge waveguide with topology protection. The valley edge state waveguide constructed by the armchair boundary can realize the directional selective transmission of chiral optical field signals, and the chiral conservation is always kept in the transmission process of the chiral optical signals. And the valley edge state waveguide constructed by combining the armchair boundary and the zigzag boundary can realize the transmission of a chiral optical field at a corner of 90 degrees and the transmission of a 180-degree corner formed by two continuous corners of 90 degrees, and no back scattering signal is lost in the transmission process.
Example 2
The embodiment 2 of the invention discloses a transmission method of a chiral optical signal, and the valley edge waveguide in the embodiment 1 is applied to the transmission of specific signals. The scheme is as follows:
a transmission method of chiral optical signals, which adopts the valley edge waveguide in embodiment 1 to transmit chiral optical signals; the transmission method comprises the following steps:
an excitation source is arranged at the center of any regular triangle hole on the boundary of the armchair;
when the excitation source is a left-handed chiral optical signal, the optical signal is transmitted leftwards along the valley edge state waveguide; when the excitation source is a right-handed chiral optical signal, the optical signal is transmitted along the valley edge state waveguide in the right direction; no back scattering signal returns in the transmission process and at the waveguide end face output;
the chiral optical signal enters the zigzag boundary at the 90-degree corner of the armchair boundary for transmission, so that the 90-degree corner of the chiral optical signal is realized; then enters the armchair boundary at a 90-degree corner of the zigzag boundary for transmission, and can realize a 180-degree corner of the chiral optical signal.
An excitation source can also be arranged at the zigzag boundary, so that the chiral optical signal starts from the zigzag boundary and enters the armchair boundary after passing through 90 degrees.
The embodiment discloses a transmission method of a chiral optical signal, which is implemented by using the valley edge waveguide in embodiment 1 to transmit the chiral optical signal, and can realize 90-degree and 180-degree rotation angles of the chiral optical signal without back scattering signal loss in the transmission process.
Example 3
The embodiment discloses a chiral optical signal equal splitting device based on a valley edge state waveguide, which applies the valley edge state waveguide of embodiment 1 to equally split a chiral optical signal. The specific scheme is as follows:
a chiral optical signal equal beam splitting device based on a valley edge state waveguide adopts the valley edge state waveguide of embodiment 1, and combines two forms of armchair boundaries and two forms of zigzag boundaries to construct a vertical cross Gu Bianyuan state waveguide, so as to realize the equal beam splitting function of the transmitted chiral optical field signal intensity.
The beam splitting device comprises boundaries of four forms, namely an SSBB form boundary, a BBSS form boundary, an SS form boundary and a BB form boundary. One of the SSBB format boundary and the BBSS format boundary is used for carrying an excitation source of the chiral optical signal, and the other of the SSBB format boundary and the BBSS format boundary is used for guiding the chiral optical signal to split equally to both sides.
In the first direction, the SSBB form boundary and the BBSS form boundary are connected at a preset beam splitting point; in a second direction, the SS and BB form boundaries join at a beam splitting point; the first direction is perpendicular to the second direction.
After a chiral optical signal enters a beam splitting point from the armchair boundary in one form, the chiral optical signal cannot enter the armchair boundary in another form based on a chiral conservation principle; and two forms of zigzag boundaries exist at the beam splitting point, and the transmission directions of the chiral optical signals in the two forms of zigzag boundaries after beam splitting are opposite, so that equal beam splitting is realized.
Description figure 7 shows that the boundaries of armchair and zigzag boundary of zigzag are crossed vertically Gu Bianyuan waveguide to realize the equal beam splitting function of the transmitted chiral optical field signal intensity. Fig. 8 is a schematic diagram of the effect of beam splitting of the optical field signal. The vertical direction is the armchair boundary, and the boundary form from top to bottom is as follows: SSBB-BBSS; the horizontal direction is zigzag boundary, and the boundary form from left to right is as follows: BB-SS. The excitation source is positioned in the center of the first small S regular triangular hole on the SSBB form boundary, excites the right-handed chiral optical field signal and transmits the right-handed chiral optical field signal along the armchair boundary valley edge state waveguide, and equal beam splitting of the right-handed chiral optical signal intensity is realized at the intersection point of the right-handed chiral optical field signal and the zigzag boundary. The transmitted right-handed optical field signal does not continue along the boundary of the lower half BBSS pattern, but is split equally in intensity at the crossing point, one SS pattern along the zigzag boundary of zigzag is transmitted to the right, and the other BB pattern along the zigzag boundary of zigzag is transmitted to the left. 5363 the characteristic of the Gu Bianyuan mode waveguide transmission is to keep the conservation of chirality during the transmission process, while the SSBB form of armchair boundary is opposite to the BBSS form chirality, therefore, the chiral optical field will not continue to want the next half armchair boundary transmission. After the intersection is divided, the SS form and the BB form of zigzag boundaries of zigzag are opposite in chirality, and the transmission directions of the divided beams along the SS and BB are also opposite, so that the right-handed chiral optical field is divided into two beams to be transmitted along the SS and BB respectively. And at the intersection point, the intensities of the beams split to the Zigzag boundaries of the two SS and BB forms are equal, and the beam splitting geometry of its 90 ° angle determines the case of equal intensity splitting of the propagating chiral optical signal.
The invention discloses a valley edge state waveguide adopting an armchair boundary and application thereof, and a boundary formed by two-dimensional photonic crystals with opposite structures is designed to realize chiral optical signal transmission of the valley edge state waveguide under topological protection. The valley edge state waveguide constructed by the armchair boundary can realize the directional selective transmission of the chiral optical field signal, and the chiral conservation is always kept in the transmission process of the chiral optical signal. And the valley edge state waveguide constructed by combining the armchair boundary and the zigzag boundary can realize the transmission of a chiral optical field at a corner of 90 degrees and the transmission of a 180-degree corner formed by two continuous corners of 90 degrees, and no back scattering signal is lost in the transmission process. By constructing a vertical crossing structure of the armchair boundary and the zigzag boundary, a valley edge state waveguide beam splitting device protected by a two-dimensional photonic crystal topology is formed, and the beam splitting function of equally dividing the intensity of the transmitted chiral optical field signal at the vertical crossing point is realized.
Those skilled in the art will appreciate that the drawings are merely schematic representations of preferred embodiments and that the blocks or flowchart illustrations are not necessary to practice the present invention. Those skilled in the art will appreciate that the modules in the devices in the implementation scenario may be distributed in the devices in the implementation scenario according to the description of the implementation scenario, or may be located in one or more devices different from the present implementation scenario with corresponding changes. The modules of the implementation scenario may be combined into one module, or may be further split into multiple sub-modules. The above disclosure is only for a few concrete implementation scenarios of the present invention, however, the present invention is not limited to these, and any variations that can be considered by those skilled in the art are intended to fall within the scope of the present invention.
Claims (10)
1. A valley edge state waveguide adopting an armchair boundary is characterized by being constructed in a graphene-like two-dimensional photonic crystal based on valley spin; the graphene-like two-dimensional photonic crystal comprises two hexagonal lattice primitive cells with opposite structures, namely a first hexagonal lattice primitive cell and a second hexagonal lattice primitive cell;
each hexagonal lattice primitive cell is composed of six sub-lattices in total, wherein one sub-lattice is composed of large regular triangle holes, and the other sub-lattice is composed of small regular triangle holes;
the Gu Bianyuan modal waveguide comprises an armchair boundary, which can be divided into an SSBB form boundary and a BBSS form boundary;
defining a preset direction, a first direction and a second direction in the same plane, wherein the first direction and the second direction are respectively vertical to the preset direction and opposite to each other;
along the preset direction, the SSBB form boundary is sequentially formed by a boundary between two adjacent small regular triangle holes and a boundary between two adjacent large regular triangle holes, the first hexagonal lattice primitive cell is positioned in the first direction of the SSBB form boundary, and the second hexagonal lattice primitive cell is positioned in the second direction of the SSBB form boundary;
along predetermineeing the direction, BBSS form boundary comprises the boundary between two adjacent big regular triangle holes and the boundary between two adjacent little regular triangle holes in proper order, and the second hexagonal lattice primitive cell is located the first direction on BBSS form boundary, first hexagonal lattice primitive cell is located the second direction on BBSS form boundary.
2. The valley edge state waveguide of claim 1, wherein the hexagonal lattice primitive cell is a regular hexagon, and the side length of the hexagonal lattice primitive cell is a:
the range of the side length of the small regular triangle hole is 0.3a-0.45a, and the range of the side length of the large regular triangle hole is 0.5a-0.7a.
3. The valley edge state waveguide of claim 1, wherein the Gu Bianyuan state waveguide is transmissive to a chiral optical signal;
the excitation source of the chiral optical signal can be located at the center of any regular triangle hole in the armchair boundary.
4. The valley edge mode waveguide of claim 3, wherein the excitation source is capable of exciting a chiral optical signal having a circularly polarized characteristic in the direction of the electric field, and is divided into a left-handed chiral excitation source and a right-handed chiral excitation source according to the direction of rotation of the circularly polarized electric field;
a left-handed chiral excitation source is arranged at the central position of a first small regular triangle hole on the boundary of the SSBB form, so that a chiral optical signal propagating leftwards can be excited;
a right-handed chiral excitation source is arranged at the central position of a first small regular triangle hole on the boundary of the SSBB form, so that a chiral optical signal propagating rightwards can be excited;
a left-handed chiral excitation source is arranged at the central position of a first large regular triangle hole on the BBSS type boundary, so that a chiral optical signal propagating leftwards can be excited;
a right-handed chiral excitation source is arranged at the center of the first large regular triangle hole of the BBSS type boundary, so that a chiral optical signal propagating to the right can be excited.
5. The valley edge mode waveguide of claim 1, wherein said Gu Bianyuan mode waveguide further comprises a zigzag boundary;
the linking of the armchair borders with the zigzag borders allows to realize 90 ° corners and 180 ° corners of the signal.
6. The valley edge state waveguide of claim 5, wherein said zigzag boundary is divided into a BB boundary and an SS boundary;
in a valley edge mode waveguide at a 90 ° corner:
if the armchair boundary in the horizontal direction is the SSBB type boundary:
the SS form boundary is jointed at a 90-degree corner of the SSBB form boundary, so that the right optical rotation signal can be upwards propagated along the SSBB form boundary;
by joining the boundaries of the SSBB forms at 90 ° corners of the boundaries of the SSBB forms, it is possible to realize that the right optical rotation signal propagates down the boundaries of the SSBB forms.
7. The valley edge waveguide of claim 6, wherein the right-handed optical signal 180 ° turn is achieved by joining the zigzag boundaries at 90 ° turn of the SSBB-type boundaries and joining the BBSS-type boundaries at 90 ° turn of the zigzag boundaries.
8. A method for transmitting a chiral optical signal, comprising using the valley edge state waveguide of claim 1; the transmission method comprises the following steps:
an excitation source is arranged at the center of any regular triangle hole on the boundary of the armchair;
when the excitation source is a left-handed chiral optical signal, the optical signal is transmitted leftwards along the valley edge state waveguide; when the excitation source is a right-handed chiral optical signal, the optical signal is transmitted along the valley edge state waveguide in the right direction; no back scattering signal returns in the transmission process and at the waveguide end face output;
the chiral optical signal enters the zigzag boundary at the 90-degree corner of the armchair boundary for transmission, so that the 90-degree corner of the chiral optical signal is realized; then enters the armchair boundary at a 90-degree corner of the zigzag boundary for transmission, and can realize a 180-degree corner of the chiral optical signal.
9. A chiral optical signal equal splitting device based on a valley edge state waveguide, which is characterized by comprising the valley edge state waveguide of any one of claims 1 to 7;
the beam splitting device comprises an SSBB form boundary, a BBSS form boundary, an SS form boundary and a BB form boundary, and an excitation source of a chiral optical signal is positioned at the SSBB form boundary or the BBSS form boundary;
in a preset first direction, the SSBB form boundary and the BBSS form boundary are connected at a preset beam splitting point;
in a preset second direction, the SS form boundary and the BB form boundary are jointed at the beam splitting point;
the first direction is perpendicular to the second direction.
10. The equal splitting device for the chiral optical signal according to claim 9, wherein after the chiral optical signal enters the splitting point from one armchair boundary, the chiral optical signal does not enter another armchair boundary based on the principle of chiral conservation;
and two forms of zigzag boundaries exist at the beam splitting point, and the transmission directions of the chiral optical signals in the two forms of zigzag boundaries after beam splitting are opposite, so that equal beam splitting is realized.
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